Extraction of thermalized projectile fragments from a large volume gas cell

Experiments to determine the stopping and extraction efficiency of energetic (90 MeV/u) 76Ga fragments in a 1.2 m long gas cell filled with helium at 123 mbar are reported. The thermalized ions were transported by DC and RF fields as well as gas flow, then jetted through a supersonic nozzle into a RF quadrupole ion-guide and accelerated into an electrostatic beam line. The ions were collected in either a Faraday cup or a silicon beta-detector immediately after acceleration or after magnetic analysis. The range distributions of the ions and extraction efficiency of the system were measured for different implantation rates and compared with the theoretically calculated values. The singly charged 76Ga ions were observed as [76Ga(H2O)n]+ molecular ions with n=0, 1, and 2. The stopping efficiency and the extraction efficiency were obtained from the measured distributions and compared to previous results from other devices.